In the game Persona 3: FES there is a "Secret Boss"; one that is SO hard to beat it can take up to TWO WHOLE WEEKS to just PREPARE to fight it! I am not joking. Two... weeks. If you make a single mistake you die immediately. Even after you finally finish preparing to fight this ungodly boss you have to fight it, and beating it requires as much luck as it requires patience and skill. Well, that's my answer.